1. Field of the Invention
The present invention relates to a wrench with a fixed maximum operational torque to prevent damage to the object secured by a fastener driven by the wrench.
2. Description of the Related Art
FIG. 15A of the drawings illustrates a conventional wrench 1 having a hexagonal driving portion with six planar faces 2 for engaging with six faces of a hexagonal groove in a top face of a fastener. However, slide tends to occur between the planar faces 2 of the driving portion of the conventional wrench 1 and the faces of the fastener. FIG. 15B illustrates a so-called TROX wrench 3 having plural arcuate faces 4 for engaging with corresponding arcuate faces in a top face of a fastener. Such a TROX wrench 3 is used to tighten important parts of a cars and cutting tools. As illustrated in FIG. 16, a blade 7 is tightened to a cutting tool 5 by a bolt 6. However, the expensive blade 7 tends to be damaged when the bolt 6 is excessively tightened. But the blade 7 could fly away and thus cause injury if the bolt 6 is not tightened to the desired extent.
An object of the present invention is to provide a wrench with a fixed maximum operational torque such that when the torque applied by the user is greater than the maximum operational torque, the wrench slides and the fastener is not turned. Thus, damage to the object secured by the fastener resulting from over-tightening is prevented.
Another object of the present invention is to provide a wrench with a fixed maximum operational torque that can be altered in response to the actual use.
In accordance with the present invention, a wrench comprises a rod, a retainer, a pressing member, and a casing for accommodating the retainer and allowing relative pivotal movement between the casing and the retainer. The pressing member is received in the casing and slidable along a longitudinal direction of the rod. The pressing member is biased to press against two ends of the retainer, thereby exerting an engaging force between each of two ends of the retainer and an associated one of the ends of the pressing member. When a rotational force applied to the casing is smaller than the engaging force, the retainer and the rod are turned to thereby turn the fastener. When a rotational force applied to the casing is greater than the engaging force, the casing and the pressing member slide while the retainer and the rod are not turned.
Other objectives and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.